1. Field of the Invention
The present invention relates to an absorbent article such as a disposable diaper, a sanitary napkin, a pantie liner or a urine absorbing pad and, more particularly, to an absorbent article using a back sheet having regions, which are different in the degree of orientation, and a method for manufacturing the back sheet.
2. Related Art
In order to absorb discharges, there have been recently employed a number of absorbent articles such as disposable diapers, sanitary napkins, pantie liners or urine absorbing pads. When a discharge is made while the absorbent article is worn, the absorbent article having absorbed the discharge is disposed of and is replaced by a new one.
Here, the back sheet to be ordinarily employed in the absorbent article is exemplified by a liquid-impermeable resin sheet. The back sheet is formed by stretching a resin film containing an inorganic filler so as to enhance the air-permeability and the moisture-permeability so that the back sheet is made opaque. In the case of the diaper, therefore, in order to confirm whether or not the wearer has made a discharge, the care taker has to remove the diaper from the wearer to confirm the inside of the diaper. This is a seriously troublesome work for the care taker.
In Unexamined Published Japanese Patent Application No. 5-168660, therefore, there is disclosed a uniaxially oriented air-permeable film which is embossed to have a moisture-permeability of 1,000 g/m2/24 hrs or more so as to enhance the optical transmittance. In this film, however, the moisture-permeability is not so lowered that the optical transmittance cannot be enhanced so high.
In Unexamined Published Japanese Patent Application No. 10-85257, on the other hand, there is disclosed a back sheet of a developing type disposable diaper. In this back sheet, a see-through portion is formed in at least a central portion in the longitudinal direction. This back sheet is formed like before of a porous sheet, which is prepared by stretching the resin film containing the inorganic filler, for enhancing the moisture-permeability. In the see-through portion, a transparent portion is formed by crushing the pores of the porous sheet by an embossing treatment thereby to eliminate the scattering of light. If the porous sheet is further embossed, however, pin holes will be easily formed, because the embossed portion is lowered in its strength. There is also a description that the transparent portion could be formed by applying wax, varnish or hot melt in place of the embossing treatment. However, the applied material will ooze or stick on the film surface and requires a drying treatment after applied, so that the cost for the material and for the treatment rises.
Thus in the disposable diaper, there has been demanded a back sheet which is so enhanced in the optical transmittance that whether or not the discharge has been made can be confirmed from the outside without lowering the air-permeability, the moisture-permeability or the strength.
Here will be described a sanitary napkin. This sanitary napkin may be provided on the two longitudinally extending sides with wings which extend in the width direction. When the sanitary napkin is worn, the wings are folded back to the lower side of the crotch portion of the underwear such as panties so that the edge portions of the panties can be prevented from being blotted with the discharge. Moreover, the napkin can be prevented from going out of position by adhesion means disposed on the wings for attaching the napkin to the panties. These wings are formed by protruding the member constructing the body of the napkin, such as the adhered back sheet and top sheet, in the width direction from the two side portions of the body of the napkin.
In the back sheet of the sanitary napkin, however, the back sheet is formed as in the diaper by stretching the film so as to enhance the air-permeability so that the optical transmittance is extremely lowered. When the panties wearing the napkin with the wings is seen from the outside, therefore, the presence of the wing portions, i.e., the wearing of the napkin is apparent from the outside. Only the wings could be made of a material different from that of the back sheet, such as a high optical transmittance sheet so that the wearing of the napkin could not be confirmed in the appearance. However, this makes the manufacture process complex to raise the cost.
Thus, the absorbent article has been desired to have a partially high optical transmittance. However, the portion desired to have a high optical transmittance is different among the kinds of absorbent articles.